Abnormal Karyotype and Prognosis in Polycythemia Vera: A Single Center Experience in 239 Informative Cases

Background

In polycythemia vera (PV), abnormal karyotype at diagnosis has been reported in 10% to 20% of patients and some studies have suggested an association with inferior survival (Leukemia2013;27:1874) . In the current study, we examined the prognostic contribution of abnormal karyotype, in general, and specific abnormalities, in particular, in newly diagnosed PV.

Methods

Study patients were selected from our institutional database of myeloproliferative neoplasms (MPN) and fulfilled the 2008 World Health Organization (WHO) criteria for diagnosis of PV (Blood. 2009;114:937). Cytogenetic analysis and reporting was done according to the International System for Human Cytogenetic Nomenclature (Cytogenetic and Genome Research2013;141:1-6). Assignment as "unfavorable karyotype" was according to criteria established for PMF: favorable = normal + favorable abnormalities; unfavorable = unfavorable abnormalities (Leukemia. 2011;25:82). Screening for the two most frequent mutations in PV, other than JAK2 (i.e. TET2 and ASXL1), were performed according to conventional methods (Leukemia. 2014;28:2206). Statistical analyses considered clinical and laboratory parameters obtained at time of diagnosis.

Results

Patient characteristics:

Median (range) values for the 239 study patients (53% females) included: age 62 (17-94), leukocyte count 11.7 x 10(9)/L (4.3-59.3) and platelet count 479 x 10(9)/L (37-2747). Palpable splenomegaly was present in 26% of the patients, pruritus in 27%, erythromelalgia in in 8%, hypertension in 47%, diabetes in 10% and hyperlipidemia in 28%. Thrombosis history at diagnosis was documented in 33% of the patients and 20% experienced the same after diagnosis. 73% of the patients were "high risk" by conventional risk stratification. Mutation screening for TET2 and ASXL1 was performed in 80 patients and mutational frequencies were 19% and 11% respectively. All study patients provided cytogenetic information, which was abnormal in 46 (19%) patients. The most frequent abnormalities were isolated +9 (n=11; 24% of abnormal karyotype and considered favorable), isolated del(20q) (n=8; 17% of abnormal karyotype and considered favorable), isolated loss of Y chromosome (n=7; 15% of abnormal karyotype and considered favorable) and isolated +8 (n=5; 11% of abnormal karyotype and considered unfavorable). A total of 9 (20% of abnormal karyotype) patients displayed unfavorable karyotype that included +8 in 7 patients, del(11q) in one patient and +20 in one patient. After a median follow-up of 83 months, 70 (29%) deaths, 48 (20%) thrombotic events, 20 (8%) fibrotic progressions and 7 (3%) leukemic transformations were documented.

Comparison of patients with and without cytogenetic abnormalities

Patients with abnormal cytogenetics were older (p=0.048), displayed lower platelet count (p=0.005) and were more likely to be high risk (p=0.02); there was no significant correlation with TET2 or ASXL1 mutation. In univariate analysis, patients with abnormal cytogenetics displayed inferior leukemia-free (p=0.007; HR 10.6, 95% CI 1.9-58.7), myelofibrosis-free (p<0.0001; HR 7.7, 95% CI 3.1-19.3) and overall (p=0.13; HR 1.6, 95% CI 0.9-2.8) survival. Furthermore, the difference in overall survival became significant when cytogenetic abnormalities were classified into unfavorable (p=0.006) and favorable (p=0.6) categories. On the other hand, inferior leukemia-free and myelofibrosis-free survival was noted in both patients with favorable and unfavorable cytogenetic abnormalities, when compared to normal karyotype. During multivariable analysis that included age and leukocytosis (≥15 x 10 (9)/L) as covariates, the adverse effect of abnormal cytogenetics on leukemia-free (p=0.009) or myelofibrosis-free (p<0.0001) survival and that of unfavorable karyotype on overall (p=0.05) survival were shown to be independent. Finally, patients with abnormal cytogenetics were less likely to experience thrombosis after diagnosis (p=0.04; HR 0.3, 95% CI 0.09-0.97), an effect that was independent of both age and thrombosis history.

Conclusions

Cytogenetic abnormalities in PV confer an independent adverse prognostic effect on overall, leukemia-free and myelofibrosis-free survival, but not thrombosis-free survival; the adverse effect on leukemia-free and myelofibrosis-free survival was seen with both favorable and unfavorable cytogenetic abnormalities.